Genetic composition of a population of natural common bream Abramis brama × roach Rutilus rutilus hybrids and their morphological characteristics in comparison with parent species: characteristics of a. brama × r. rutilus hybrids

Common bream Abramis brama, roach Rutilus rutilus and their hybrids were collected in the Dobczyce Reservoir in southern Poland in 2006-2013 to study whether it is better for a hybrid individual to resemble and compete with one of its parents, or to minimize competition by having a distinctive phenotype. All hybrids were F1 crosses and originated predominantly (93·2%) from matings between female A. brama and male R. rutilus parents. In morphometric analyses, a newly defined coefficient, L3  = 2·5 (body mass) (LS  × body depth)-1 , which enables forms with similar length-depth proportions but different length-mass relationships to be distinguished was used. Morphometric and meristic characteristics of the hybrids were intermediate in comparison with the parental species, with small but significant deviation towards R. rutilus in longitudinal body dimensions (trunk and tail length) and towards A. brama in body cross-sectional shape (body depth and L3 coefficient). This may result in a more R. rutilus like propulsion in hybrids and a more A. brama like ability to manoeuvre.